It is not necessarily true that dogs with light pigment or white dogs are all deaf. nor is it true that a dog with a black spot around its eye/on its ear etc is NOT deaf. Here is what is known about the cause of congenital deafness in dogs.

"The deafness, which usually develops in the first few weeks after birth while the ear canal is still closed, usually results from the degeneration of part of the blood supply to the cochlea (the stria vascularis). The nerve cells of the cochlea subsequently die and permanent deafness results. The cause of the vascular degeneration is not known, but appears to be associated with the absence of pigment producing cells (melanocytes) in the blood vessels."

Yes, that is true. They cannot yet link it to a specific color gene. The two color genes that people will agree on that can be linked to deafness are the piebald and merle genes. Deaf dobermans do not carry either of those color genes.